NCSU GIS/MEA582:
Geospatial Modeling and Analysis

Data display and visualization

Resources:

• GRASS GIS overview and manual
• Recommendations and tutorial how to use wxGUI from the first assignment
• Screen captures for 3D visualization with wxnviz in GRASS6.4.3RC2 (similar to GRASS7)
  • Visualization in GRASS I: surface (71MB)
  • Visualization in GRASS II: draping points and lines (45MB)
  • Visualization in GRASS III: cutting planes (62MB)

Start GRASS GIS

grass70

Visualization in 3D perspective

g.region raster=elevation -p 

Interactively view "elevation" raster and vector data ("streams", "usgsgages") in 3D view, adjust viewing position, surface properties and lighting to highlight features.

Remove or switch off any map layers in the Layer Manager. Then add raster "elevation", Add vector "streams", Add vector "usgsgages".
Zoom to computational region and Switch to 3D view.

Follow the video Visualization I and II for similar tasks (link is above) and save 2-3 images for your report (save as tiff or take screenshot, if you don't have tiff support).

Visualizing multiple surfaces

It is recommended to quit GRASS before starting the task below because we will be working with a smaller, high resolution region.

Start GRASS7 with your previous MAPSET. First set region to "rural_1m", then interpolate surface with vegetation from multiple return lidar points using the module v.surf.rst (we will explain interpolation later on).

g.region rural_1m -p
v.surf.rst elev_lidrural_mrpts elevation=elev_lidruralmr_1m npmin=120 segmax=25 tension=40 smooth=1.0

In Layer Manager Add rasters "elev_lidruralmr_1m" and "elev_lid792_1m" (bare earth). In Map Display Zoom to computational region.

Make sure that you have only the two elevation maps switched on in the Layer Manager. Switch to 3D view and follow the video Visualization III (link is above). Save 2-3 interesting images for your report, include at least one crossection.

Basic 2D display operations

Display subsets of data

Display land use categories 1, 2 (developed land) over shaded topography.
Settings > Region > Set region > Set region to match this raster > select "landuse96_28m".
Add raster > select "elevation_shade".
Add raster > select "landuse96_28m" > Selection > List of cats to display > 1,2.
Zoom to computational region.
Right click on "landuse96_28m" map layer and Change opacity to show topography blended with landuse. Save display to graphic file. You may want to remove all previously used layers from the Layer Manager before you start visualizing the new ones.

g.region raster=landuse96_28m -p

d.rast elevation_shade
d.rast landuse96_28m values=1,2
d.out.file landuse_elev

Change colors for raster maps

First create your own copy of the elevation map (see the command below).
Display it by Add raster > "myelev".

g.copy raster=elevation,myelev
d.rast myelev

Set the color table to a predefined one, for example "bgyr" (blue, green, yellow, red).

GUI options: Right Click on the raster layer "myelev" in Layer Manager > Set color table > Define > Name of color table > "bgyr" > Run.
If you don't see the new colors - click the second button in Map Display to redraw.

r.colors myelev color=bgyr
d.rast myelev

Change the color table interactively using rules:

In the Layer Manager manu click Raster > Manage colors > Manage Color rules interactively.
Select raster map "myelev".
Click on colored squares to change the color, click Preview.
If it looks good - click OK.

To create color table for future multiple uses type the rules into a plain text mycolor.txt file using a text editor (TextEdit, Notepad), for example:

50 blue
70 aqua
90 green
110 yellow
130 orange
160 brown

Then assign it as follows:
Right click on "myelev" map layer > set color table > Define > Path to rules file > Run.
If needed, redraw using the second button on Map Display. You can also create and assign the above color table by typing or pasting it into the enter values interactively window or run it from comand line (make sure you have the correct path, in the following example mycolor.txt should be replaced by e.g. /Users/john/mycolor.txt on Mac OS X):

r.colors myelev rules=mycolor.txt

Note that you can combine color RGB and name definitions as well as % and cat/val to create complex custom color tables and store them in a text file for future use, see the examples in r.colors man page.

Compare the use of equal interval and histogram equalized color table for slope

g.copy raster=slope,myslope
r.colors myslope color=bgyr
d.rast myslope
d.legend myslope
d.out.file myslopecolor

To explain the difference between the two maps, you can generate a histogram. On map Display click on Analyze map > Create histogram to open the histogram tool and save results to graphics file. Or use this command which will add a histogram as a layer to Layer Manager.

d.histogram myslope

Now set the histogram equalized color table, and save the new slope map and histogram images. Describe the effect of the histogram equalized color table.

r.colors -e myslope color=bgyr
d.out.file myslopecolorequalized
d.histogram myslope

Modify legend, scale and grid

Note: you can use horizontal legends by using Placement at=6,10,2,30 or just stretch it horizontally with mouse.

d.barscale
d.legend myslope at=50,90,4,7

Switch off "myslope", display "myelev" raster and change the legend to "myelev" raster. Add grid for state plane coordinates at 5000m with ticks at 1000m. Also add a lat/long grid at 2 arc minute interval.

In Layer Manager > Add various overlays > Add grid layer > Size 5000 > Run.
To draw only border with ticks: change Size to 1000 and click Disable > Disable grid drawing > Run.
Switch off Disable grid drawing.
To draw lat/long grid: set Required > Size to 0:02 > click Draw > Draw geographic grid > Run.
Command line alternative:

d.rast myelev
d.legend myelev
d.grid size=5000 color=brown
d.grid -n size=1000
d.grid -g size=0:02 color=black
d.out.file myelevmap

Display color composite

d.rgb red=lsat7_2002_30 green=lsat7_2002_20 blue=lsat7_2002_10
d.vect roadsmajor color=yellow
d.out.file mylandsat

Export NC precipitation stations data to kml and post in Google Earth

g.region nc_500m
v.out.ogr precip_30ynormals output=c:\temp\precipitation.kml format=KML type=point

Optional part

Add WMS layer

g.region rural_1m -p
d.rast ortho_2001_t792_1m

In Layer Manager toolbar Add web service layer.
Paste the link to the service into server field and press connect:

http://raster.nationalmap.gov/arcgis/services/Orthoimagery/USGS_EROS_Ortho_1Foot/ImageServer/WMSServer?

To save the layer:
Right click on the web service layer in Layer Manager - choose Save web service layer. In dialog, set the name of the layer ortho_new and press Save layer.

Map Swipe

Move slider to compare images - what changes do you observe? Save a screenshot of the mapswipe window showing the comparison of orthos. See more options here.